Several tray designs are known for gas-liquid contactors used in chemical processes including reactions and separations. In each design, trays are situated within the towers for contact between the gas and liquid within the towers. Trays for large diameter towers are prone to liquid flow maldistribution on the trays as described, for example, by M. J. Lockett in “Distillation Tray Fundamentals” (1986). It is also known that liquid flow maldistribution on a tray affects tray efficiency—see Wijn, E. F. in “The effect of downcomer layout pattern on tray efficiency” published in The Chemical Engineering Journal, vol. 63, pages 167-180 (1996).
Several tray designs intended for correcting liquid flow maldistribution have been invented, of which the following are representative examples: U.S. Pat. No. 3,729,179 (1973) issued to Keller; U.S. Pat. No. 3,747,905 (1973) issued to Nutter et al.; U.S. Pat. No. 5,269,976 (1993) issued to Biddulph et al; U.S. Pat. No. 5,453,222 (1995) issued to Lee et al; U.S. Pat. No. 6,371,455 (2002) issued to Lee et al; U.S. Pat. No. 6,817,596 (2004) issued to Fischer; and U.S. Pat. No. 8,070,142 (2011) issued to Lee et al.
The above listed patents disclose various downcomer designs that allow the liquid to leave the downcomer and flow across an immediately subjacent tray in a more uniform pattern. However, because tray decks are not rectangular, some degree of maldistribution develops when the liquid travels some distance across a tray to an outlet downcomer. Unexpectedly, it was discovered that liquid entering the downcomer does not undergo lateral mixing because there is no hydraulic gradient. In a multiple tray tower, the lack of downcomer mixing can develop a concentration gradient which propagates down the tower. All prior art patents disclose downcomer distributor designs that aim at distributing liquid at the entrance of the tray to improve liquid distribution across the tray, but none include means at the top of the downcomer for ensuring that the liquid entering the downcomer has a uniform composition.
In spite of previous efforts, there still exists a need to address the maldistribution issue. The present invention addresses the maldistribution issue by providing a downcomer, which incorporates both a novel liquid mixer with a novel liquid distributor.